Voltage-Controlled Magnetic Anisotropy (VCMA)

Updated 19 August 2025

VCMA is the electric-field modulation of magnetic anisotropy at interfaces, exploiting spin–orbit coupling to control magnetization states.
It enables low-energy, rapid magnetization switching in non-volatile memories and logic devices by reducing energy barriers for reversal.
Recent advances focus on VCMA coefficient engineering via negative capacitance and quantum well integration to enhance device performance and scalability.

Voltage-Controlled Magnetic Anisotropy (VCMA) is a phenomenon wherein the magnetic anisotropy energy (MAE) of a magnetic layer is modulated via an applied electric field. By leveraging interfacial and electronic structure effects, VCMA provides a practical pathway for low-power manipulation of magnetization states in ferromagnetic, antiferromagnetic, and hybrid material systems. VCMA plays a pivotal role in energy-efficient memory, spin logic, reconfigurable magnonics, and emerging post-CMOS computational hardware.

1. Fundamental Mechanism of VCMA

VCMA exploits the ability of an external electric field to modify the energy landscape governing the magnetization orientation of a thin magnetic film—typically at the interface between a ferromagnet (FM) and an insulator (I), such as Fe/MgO or CoFeB/MgO. The effect is highly localized at the interface due to screening, making it most pronounced in ultrathin films. The change in magnetic anisotropy energy is typically modeled as:

$\Delta K = \xi E$

where

$\Delta K$ is the change in MAE,
$\xi$ is the VCMA coefficient (usually in units of fJ/V·m),
$E$ is the applied electric field across the insulator.

The microscopic origin is the electric-field-induced change in $d$ -orbital occupancy on transition metal atoms at the interface, which alters the strength of spin–orbit coupling (SOC) and, thereby, the perpendicular/planar MAE (Zhang et al., 2016). Precise control can be achieved by band-filling (alloying), interface design (e.g., clean or oxidized interfaces), and electrostatic doping (Zhang et al., 2016, Wen et al., 2016). In some instances, hole doping or particular orbital filling reverses the VCMA sign, producing the so-called "inverse VCMA" effect, with record-high coefficients exceeding 1 pJ/V·m (Zhang et al., 2016).

2. VCMA in Magnetization Switching and Spintronic Memories

VCMA enables ultralow-energy and rapid control of magnetization switching—essential for non-volatile magnetic memory (MRAM) and logic-in-memory paradigms. In voltage-assisted switching schemes, the applied field reduces the energy barrier for magnetization reversal, effectively "gating" the transition:

By combining VCMA with spin transfer torque (STT) or spin–orbit torque (SOT) in a magnetic tunnel junction (MTJ), one can achieve deterministic, field-free switching with drastically reduced current and energy requirements (down to sub-fJ levels), short write times (sub-nanosecond to few-nanosecond), and excellent thermal stability (e.g., 43 $k_B T$ at 0.45 fJ switching energy (Ghosh et al., 2014)) (Deng et al., 2017, Peng et al., 2018, Ghosh et al., 2014).
In high-density arrays, VCMA can "boost" the switching probability of selected cells while half-selected cells remain unswitched due to non-linear switching characteristics controlled by the pulse amplitude and duration, thus solving the sneak path problem in crossbars used in AI hardware (Yang et al., 2022).
Integration with topological insulators invokes exchange torques from spin-momentum-locked surface states, promoting further energy reduction and speed enhancements (Ghosh et al., 2014).

3. VCMA Coefficient Engineering and Amplification Strategies

The magnitude of the VCMA coefficient $\xi$ is a critical figure of merit. Achieving sufficient modulation at sub-100 nm device dimensions remains a challenge due to constraints on the attainable $\xi$ :

System	VCMA Coefficient ( $\xi$ )	Notable Context
Ru/Co $_2$ FeAl/MgO	108–139 fJ/V·m (RT; 4K)	High interfacial PMA and efficiency
FeB/W	~50 fJ/V·m	Confirmed by four independent methods
Graphene/Pt-porphyrin/Py (Shukla et al., 5 Jul 2025)	375.6 fJ/V·m	Functionalized 2D system
FM/Quantum Well/Oxide	>1 pJ/V·m (even-ML, QW-resonant)	A-shaped bi-polar VCMA
FM/FE/MgO (Negative Capacitance)	Amplification up to $\sim$ 350 $\times$	Negative capacitance FE amplifiers

Amplification approaches include:

Series integration of a ferroelectric (FE) layer in a negative capacitance regime with the oxide barrier, dramatically amplifying the gate voltage across the MTJ insulating layer—the effective field, and hence VCMA, can be boosted by orders of magnitude (Zeng et al., 2016, Zeng et al., 2019).
Quantum well (QW) engineering, wherein resonance near the Fermi level (especially for even atomic layer numbers) produces enhanced, sometimes bi-polar, VCMA responses (Xiang et al., 2020).
Chemical functionalization of 2D materials (Pt-porphyrin on SLG), achieving large $\xi$ due to enhanced spin–orbit coupling and interfacial effects (Shukla et al., 5 Jul 2025).

4. Applications Beyond Memory: Logic, Skyrmionics, Spin Wave and Oscillator Control

VCMA is broadly leveraged for advanced information processing concepts:

In domain wall logic architectures, VCMA defines "pinning wells" that enable reliable and localized domain wall (DW) position control, greatly improving concatenation and pipeline reliability in matrix-matrix multipliers and radiation-hard logic (Zogbi et al., 2023).
Skyrmion-based memory and logic benefit from VCMA-tuned PMA to control skyrmion creation, annihilation, and synchronization, all without external magnetic fields. In large-scale, pipelined logic, VCMA clocks release skyrmions synchronously, mitigating the limitations of geometrical notch-based clocking (Bhattacharya et al., 2019, Walker et al., 2021).
VCMA is used to manipulate phase shifts of propagating dipolar spin waves, enabling on-chip magnonic logic and energy-efficient, reconfigurable phase shifters in post-CMOS computing hardware. Phase shifts up to 2.5 $\pi$ mrad are demonstrated for Co/MgO, increasing by a factor of 200 with GdO $_x$ dielectrics (Petrillo et al., 5 Feb 2024).
In nano-constriction spin Hall nano-oscillators (SHNOs), VCMA strongly modulates the local anisotropy and effective damping, supporting frequency tuning over multi-GHz ranges and unlocking analog neuromorphic functionalities (González et al., 2022).
In voltage-controlled spin oscillators (VCSOs), the oscillation frequency and phase locking range can be efficiently modulated by VCMA and enhanced further with negative capacitance layers, simplifying mutual synchronization (Zeng et al., 2019).

5. VCMA in Antiferromagnetic Materials and Resonance Control

In antiferromagnetic (AFM) systems, VCMA expands the control paradigm beyond ferromagnets:

Gate-induced modulation of AFM anisotropy enables both linear and parametric resonant excitation of the Néel vector. VCMA-driven parametric pumping yields exchange-enhanced coupling efficiency, surpassing microwave or spin–orbit torque methods by 1–2 orders of magnitude—an effect unique to AFMs with perpendicular easy axes.
Crucially, VCMA allows for zero-field parametric resonance, an impossibility for conventional microwave pumping in these systems due to symmetry constraints. This provides avenues for coherent high-frequency excitation, ultrafast switching, and low-power operation in antiferromagnetic spintronics (Tomasello et al., 2022, Chang et al., 2020).

6. Device Physics, Symmetry, and Measurement Considerations

The effect's symmetry and polarity, as well as its measurement and operational constraints, are system-dependent:

For FeB and FeB/W systems, detailed studies show that coercivity, anisotropy field, Hall angle, and switching time vary linearly—and reversibly—with the applied gate voltage. A negative voltage increases PMA, while a positive voltage reduces it, with the sign opposite to that in Pt/Co/MgO (Zayets et al., 2018).
Quantification methods include anomalous Hall effect, resistance switching, ferromagnetic resonance, and direct ST-FMR measurements.
The robust and rapid switching enabled by VCMA requires careful voltage windowing and pulse timing to avoid unintended switching (as in crossbar write sneak path solutions (Yang et al., 2022)). The voltage window must ensure deterministic precession and high switching probability, often requiring consideration of demagnetization factors, device geometry, and system non-linearity.

7. Limitations, Challenges, and Future Directions

Despite its promise, challenges persist:

Engineering consistently high VCMA coefficients suitable for aggressive device downscaling remains nontrivial, especially in conventional MTJ stacks where experimental values saturate at $\sim$ 100–150 fJ/V·m (Wen et al., 2016). Negative capacitance, quantum well engineering, and functionalized 2D materials represent promising, but as yet not fully industrialized, pathways for exceeding this limit.
Long-term reliability and endurance under high-frequency voltage pulsing, especially regarding dielectric and interface integrity, pose integration and scaling challenges.
The complexity of multi-material stacks (e.g., inclusion of DMI, SOT, local VCMA, or AFM layers for field-free switching (Zhou et al., 2023)) necessitates precise nanoscale fabrication and interface control.
Further studies targeting the interplay of VCMA with intrinsic material properties (such as interfacial SOC, screening, redox chemistry, and strain coupling) as well as integration with CMOS-compatible architectures will define the frontiers of low-power, versatile spintronic technologies.